Process of preparing aluminates



Patented Oct. 17, 1939 2,176,444

UNITED STATES PATENT OFFICE PROCESS OF PREPARING ALUMINATES Hans Zirngibl, Bitterfeld, Germany, assignor to I. G. Farbenindustrie Aktiengesellschaft, Frankfort-on-the-Main, Germany No Drawing. Application July 2, 1938, Serial No. 217,310. In Germany July 10, 1937 Claims. (Cl. 23-52) The present invention relates to a process for ing at a temperature up to 1200 to 1300 C. preparing aluminates. For this purpose there are used known solid or Several processes are known in which, instead liquid and/or gaseous or solid and liquid reducof a comparatively costly sodium carbonate, soing agents, the material being brought into con- 5 dium sulfate and carbon are used in attacking tact at a temperature above about 800 to 1000 5 bauxite or other aluminiferous minerals. None C. with steam or carbon dioxide in addition to of these processes, however, has given a product the reducing agent. Since it is essential to conwithout a substantial content of sodium sulfide, duct the first part of the reduction at the lowest so that it has not been possible to obtain directly possible temperature, whereby as much as possible from the mass aluminate liquor free from iron, of the sulfur is simultaneously evolved directly 10 since sodium sulfide forms soluble double salts in the form of $02, the material is heated in a with the iron sulfide which is always present in the first furnace zone up to about 600 to 700 C., in liquor. Inasmuch as it has been believed that in a second zone up to about 800 to 1000 C. and in attacking clay with sulfuric acid and reducing a third zone up to about 1200 to 1300 C., the

with carbon the mixture of aluminium sulfate and first zone being preferably slightly oxidizing, the 15 sodium sulfate thus obtained, a mass free from second neutral when carbon is used and the third sulfide could not be produced, the operations have reducing. always included a refining of the sodium sulfide When only gaseous reducing agents are used, in Order to Obtain this y crystallization. t is they are applied in the second zone in deficiency not possible in this anne to preve e in order to avoid, a reduction of the sulfur di- 20 tamination 0f the aluminate liquors With ironoxide formed. The final reduction should occur It has already been attempted to Conduct the only at a temperature above 1000 C. in order to reactions in such a manner that the sulfur could exclude fo matio of sodium lfide as far as be recovered as sulfur dioxide In order to possible. If, in fact, the process is so conducted 5 achieve this either iron sulfide or another sulfide that practically only lfur dioxide is f rmed or carbon in excess 15 addedas reducing agent there is the further advantage that a formation It has been shown however that thls F f of carbon oxy-sulfide or other contact poisons cannot be so conducted that merely sulfur diox1de for the Sulfuric acid process are excluded from is produced and the residue is free from sulfide the beginning The Supervision of the first and sulfate; rather there is always produced in 30 addition to sulfur dioxide, sulfur and sulfuretted f g i gjggi fi gg ig ggi g to about hydrogen, as well as sodium sulfide and sulfate. to 2 that is to Say the carbon in the second It has further been found that if the temperature is raised above 800 to 10000 C" the yield is zone 1s also in deficiency in order to cater for favorable on account of the sintering produced. the formamor} of S02 as far as posslble- 35 For the same reasons a mixture of alkaline earth prodllct conslsts up to temperatulie of @bmlt sulfate and aluminium sulfate cannot be reduced 1000 for the greate? part alummate with Success or alkaline earth aluminate. Since most of the The conclusion is that it has not hitherto been sulfur has been expelled mass may now be 40 possible to produce a pure aluminium oxide from hearted 9 about 0 to 1300 C. wlthout danger 40 aluminiferous minerals or the aluminium sulfate h wh reby wlthald of steam or carbon obtained therefrom by admixture of alkali sulfate dloxlde complete r t -w th ib ration of or alkaline earth sulfate and reduction and subthe residual Sulfur is Obtalnedy e tsd sequent extraction of aluminate, particularly with hydrogen Produced is b t o sulfur d oxide in the recovery of the sulfur in a satisfactory manthe oxidizin 0 8- 45 her in the form of sulfur dioxide which is an In the mixture the ratio A1203 to NarO or CaO important condition for the commercial prospect to C should be calculated on the following basis: of the process. When a ratio AlzO3:NazO=1:1, practically The present invention is based on the observa- 1:11 to 1.2 with respect to the ironand titanium tion that the foregoing difficulties can be minioxide, is used, the sodium aluminate produced is mized or avoided by conducting the reduction not completely soluble in water, since a portlon of the mixture of an alumim'ferous mineral, for of the aluminate is hydrolytically dissociated. In example bauxite, alunite, aluminium sulfate or the leaching liquor, however, the whole of the aluminium sulfite with an alkali sulfate and/or alumina can be retained in solution. When an alkaline earth sulfate in stages without sinteralkaline earth sulfate is used, the ratio 55 Al203:CaO=1:1 up to about 3, corresponds with the possible aluminates CaOAlzOa, 2CaOAlzO3, 3CaOAl2O3.

The proportion of carbon should preferably be between the values expressed by the following equations:

When a higher proportion A12O3INa2O is used, correspondingly more carbon must, of course, be employed.

Al203:Na2O:C=1:1:2 to 4 AlaO3:Naz0:C=1:1.5:2.25 to- 4.5 etc.

' The kind of carbonused is also of certain importance; most suitable is clean coke, in which case about to per cent. of the total sulfur is produced directly in the form of S02. Any other kind of carbon, preferably poor in ash, may be used, and coal having a small quantity of gas is to be preferred.

The reducing furnace is preferably a rotary one with a gas-tight closure on one side and facility for introducing gas and air at various positions. Obviously, other furnaces, for instance shaft furnaces, may be used, if ducts are provided for gas and air at places corresponding with the conditions desired. The desired zones are formed in the furnace by corresponding regulation of gas and air supply.

'In attacking a bauxite containing silica there is introduced into the mixture in known manner the quantity of CaO corresponding with the content of SiOz, advantageously in the form of CaSO4. The following examples illustrate the invention, the parts being by weight:

Example 1.A mixture of 342 parts of ferruginous aluminium sulfate (referred to as dry material), 142 parts. of sodium sulfate and 30 parts of coke (85% C) is charged at the feed side of a rotary furnace heated by means of water gas. In the furnace there are formed by suitable regulation of the gas and air supply 3 zones, the positions of which are controlled by gas analysis. The first zone should be formed with a slight excess of air, the second should be neutral and the third should be kept freely reducing. The gases leaving the furnace may contain 10 per cent. of S0z and 1 per cent. of 02, the rest being water Vapor,

carbon dioxide and nitrogen; other sulfur cornpounds should not be present in the issuing gases.

The product is completely reduced, contains a.

small proportion of carbonate and the iron in the form of insoluble iron sulfide which in consequence of its pyrophoric property is converted in contact with air into iron oxide. The aluminate is treated in counter-current with a leaching liquor whereby a solution practically quite free from sulfide and iron is obtained. The working-up of the product to pure alumina and sodium carbonate or sodium hydroxide follows the known methods. The gases leaving the furnace are mixed with 40 to 50 per cent. of air and worked up to sulfuric acid by the contact process, which acid may be used for attacking a further batch of mineral. Instead of the water gas prescribed above there may be used hydrogen,illuminating gas, producer gas, coal dust or the like.

If in this example the final temperature is about 1200 0., sodium sulfate formed from iron sulfate must be expected as an impurity in the aluminate liquor. If, however, the temperature is raised to about 1300 0., even the sulfur of the iron sulfide is expelled, so that only iron oxide is present.

Example 2.-A mixture of 666 parts of ferruginous aluminium sulfate (AJ2(SO4)3, 18H2O), 272 parts of calcium sulfate and 32 parts of gas coke is charged into a rotary furnace fired by coal dust. By suitable regulation of the gas and air supplies 3 zones (final temperature about 1300 C.) are formed, their position being controlled by gas analysis. The first zone is oxidizing, the second neutral and the third reducing. The gases leaving the furnace contain in addition to steam, carbon dioxide and nitrogen, about 10 per cent. of sulfur dioxide and 1 per cent. of oxygen. The calcium aluminate produced, which is sintered after the reduction, is practically quite free from sulfur and contains in addition to iron oxide only impurities due to the ash of the, coke. The comminuted product is easily leached. It may be run while hot into a sodium carbonate solution. Preferably, an excess of about per cent. of sodium carbonate is used and this may contain some sodium hydroxide and should be used in countercurrent.

Example 3.-A mixture of 666 parts of ferruginous aluminium sulfate, 104 parts of calcium sulfate, 31.3 parts of sodium sulfate and 26 parts of coke may be treated in a manner corresponding with that described in Example 2.

The invention is not limited to the exact details described, for obvious modifications will occur to a person skilled in the art. As to the final reduction in the presence of steam and/or carbon dioxide I wish to be understood that usually a sufficient quantity already results from burning a part of the gaseous reducing agent for'the interior heating of the furnace.

' What I claim is:

1. The process of preparing aluminates which comprises directly heating a mixture of a member of the group consisting of bauxite, alunite, aluminium sulfate, aluminium sulfite with a member of the group consisting of alkali and final reduction being carried out only with a gaseous reduction agent in the presence of a member of the group consisting of steam and carbon dioxide.

2. The process of preparing aluminates which comprises directly heating a mixture of aluminium sulfate and sodium sulfate, the ratio be tween A12O3 and NazO being about 1:1, in an oxidizing atmosphere to about 600 to about 700 C. and reducing the mixture in steps without sintering at a temperature up to about 1200 to about 1300 C., the chief reduction being carried out below about 1000 C. with an undercharge of the reducing agent, the final reduction being carried out only with a gaseous reduction agentin the presence of a member of the group consisting of steam and carbon dioxide.

3. The process of preparing aluminates which comprises directly heating a mixture of aluminium sulfate and calcium sulfate, the ratio between A1203 and CaO being 1:1 to 3, in an oxidizing atmosphere to about 600 to about 700 C. and reducing the mixture in steps without sintering at a temperature up to about 1200 to about 1300 C., the chief reduction being carried out below about 1000 C. With an undercharge of the reducing agent, the final reduction being carried out only with a gaseous reduction agent in the presence of a member of the group consisting of steam and carbon dioxide.

4. The process of preparing aluminates which comprises directly heating a mixture of a member of the group consisting of bauxite, alunite, aluminium sulfate, aluminium sulfite with sodium sulfate and calcium sulfate, in an oxidizing atmosphere to about 600 to about 700 C. and reducing the mixture in steps without sintering at a temperature up to about 1200 to about 1300 C., the chief reduction being carried out below about 1000 with an undercharge of the reducing agent, the final reduction being carried out only with a gaseous reduction agent in the presence of a member of the group consisting of steam and carbon dioxide.

5. The process of preparing aluminates which comprises directly heating a mixture of aluminium sulfate, sodium sulfate and calcium sulfate, in an oxidizing atmosphere to about 600 to about 700 C. and reducing the mixture in steps without sintering at a temperature up to about 1200 to about 1300 C., the chief reduction being carried out below about 1000 C. with an undercharge of the reducing agent, the final reduction being carried out only with a gaseous reduction agent in the presence of a member of the group consisting of steam and carbon dioxide.

HANS ZIRNGIBL. 

